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David-aviator

Well Known Member
Would a moderator please delete the entire thread "Hypothesis...." on paint blisters. The theory that MEK changes the chemistry of the sealant is in total error. Thank you, David Edgemon.

David Edgemon wrote:

I've built 2 RV's. Thats 4 tanks, with no, Thats NO blisters. The first plane, 9A was completed in 2004, 500 + hours and NO blisters.

What does that have to do with MEk, I thinned every batch with MEK during application (I know, my airplane is going to explode).

I also painted the thinned sealant onto all of the rivet tails so that they are fully encapsulated.

So I would humbly suggest that you look T your selant application technique, not your paint prep.

Further evidence that this is true lies with the clean up paper towels I used yesterday after building a test strip. They were soaked in MEK, the sealant on them cured over night. It's properties are essentially unchanged, at least visually and as far as I can tell.

Again, thanks dedgemon for sharing your knowledge and experience on this matter.
 
Rick Galati speaks the truth on this matter....

Some people refuse to accept that it is nothing more than poor workmanship in proseal application technique that causes paint blisters to develop. The blisters develop because fuel or its fumes migrate though an improperly prepared barrier of proseal when the fuel tanks are constructed. Gimmicks like Locktite are nothing more than a bandaid fix that address a problem that should never arise in the first place. Slight pressurization occurs in properly constructed fuel tanks and I find it curious and vindicating that if second hand reports are to be believed, even Van's seems to be grudgingly coming around to accept what I have insisted from day one in multiple posts on the famous paint blister thread started nearly 6 years ago:

http://www.vansairforce.com/communit...=paint+blister

And I would remind those doubters that even the pros can sometimes get it wrong as post #100 in that thread so graphically demonstrates:

http://www.vansairforce.com/communit...&postcount=100

Properly constructed fuel tanks using industry accepted proseal application techniques will not blister the paint and that inconvenient truth is for some RV builders a difficult pill to swallow.
__________________
Rick Galati
RV6A N307R"Darla!"
RV-8 N308R "LuLu"
EAA Technical Counselor
 
As another data point: Years ago when I built my tanks, I threw my ProSeal covered clecos into a clean paint can half full of MEK. At the end of the build session, I pounded on the cover to the can with the intention of cleaning the clecos a little later. Well, I forgot all about the can until some number of weeks later. When I eventually opened the can up, I found the proseal had cured on the submerged clecos. Interesting!!
 
noelf said:
As another data point: Years ago when I built my tanks, I threw my ProSeal covered clecos into a clean paint can half full of MEK. At the end of the build session, I pounded on the cover to the can with the intention of cleaning the clecos a little later. Well, I forgot all about the can until some number of weeks later. When I eventually opened the can up, I found the proseal had cured on the submerged clecos. Interesting!!
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Interesting, indeed.

I wonder if there is a difference in how ProSeal and ACETONE work.

Last week I dropped a couple sealant gunked-up rivet sets pieces into some ACETONE over night and by golly they were clean the next morning. It was an open can and the ACETONE had evaporated over night......maybe I imagined the event....some days I am amazed at how much I don't know?!
 
And yet another data point.....

I am familiar with one instance... an RV-10 Q.B. kit that had been completed by a professional hired gun builder.
Blisters developed on the fuel tanks.
Entirely new fuel tanks were built by a well respected builder who specializes in assembling RV fuel tanks.
The new tanks were installed and then painted by the professional painter that had originally painted the airplane.

8 months later... fuel tank blisters on the new fuel tanks.

So, in at least this one case, blisters occurred on fuel tanks built at totally different times, by totally different people, likely using at least slightly different processes. The only common factor was the painter and the paint products/process used.

I do not mean to imply that I think it is always the paint processes fault, but what I do think, is that there is not one single cause.
I think that of all of the instances where people have experienced this problem, that it has happened for a variety of different reasons. If I am correct, it explains why it has been hard to pin down and find a way to prevent it from happening.

There have been lots of opinions presented, that lean towards the assembly technique and proper application of sealant being the cause.
Personally, I think it is something else (though I don't know what) causing it.
The reason I feel that way is this...
I have been involved in the construction of RV's for 24+ years. Other people had been building RV's long before I got involved. For the most part, all of these people were amateurs, with no special training in aircraft construction. They new nothing about Mil Spec processes for doing sealant application etc., but they have built thousands of airplanes, that have been flying for many years and have never had a tank blister (other than were an obvious leak occurred at a rivet).
It is only within the past few years that this has begun to occur (though still only a small percentage of the recently completed airplanes have experienced this)

So what then is the cause? I don't know, but I am convinced that if we do ever discover the cause, it wont be a single smoking gun that we can blame on all the occurrences of the blister problem.
 
rvbuilder2002 said:
So, in at least this one case, blisters occurred on fuel tanks built at totally different times, by totally different people, likely using at least slightly different processes. The only common factor was the painter and the paint products/process used.
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Scott, this is interesting new info.

I wonder if there is any time frame correlation with EPA mandated changes in paint formulas ???

Could all of us been barking up the wrong tree?
 
So what do you do about leaky fuel tanks that Van's contractors made?? You can't get inside and patching the outside is sketchy at best.
Arrrggg! :mad:
 
Mike S said:
I wonder if there is any time frame correlation with EPA mandated changes in paint formulas ???
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I feel pretty certain that this is the cause of at lease some of the instances of blisters (but I have no strong evidence to prove that).
I do know that a lot has changed in the formulation of paints.
I have seen paints being marketed under a popular trade name, and having been popular with home builders for many years for painting their RV's, (paints that weren't specifically marketed for use on aircraft) suddenly have an obvious change in susceptibility to staining from dye in 100LL, 5606, etc.

I know that a lot of the instances of blisters have been the paint delaminating from the primer undercoat, but the primer still having good adhesion to the rivet area.
What does this mean. I don't know for sure, but to me it indicates that the crosslinking process between the primer and paint has failed to happen properly.
I don't know what the cause is, but one could be the strict requirements the paint manufacturers have regarding maximum cure time limit of the primer before it gets top coated. Some are less than 24 hours. (BTW, this one issue by it self shows that it is a bad practice (and a waste of time and money), to prime the exterior of parts during the building process. For good paint adhesion, you would need to re-prime all of those surfaces with fresh primer just before painting.
 
JDanno said:
So what do you do about leaky fuel tanks that Van's contractors made?? You can't get inside and patching the outside is sketchy at best. Arrrggg! :mad:
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Yes, you can get inside. You cut a 5" round hole in the rear wall of each bay and close it later with a 6.5" cover plate, closed-end blind rivets, and sealant. You can reach everything and seal everywhere. In one respect it is better than building new tanks; it allows the installation of a proper fillet along the skin/rear wall joint.
 
Mike S said:
I wonder if there is any time frame correlation with EPA mandated changes in paint formulas ???
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I suspect the new formulas simply yield a less permeable paint membrane.

The addition of clear coats means the paint membrane is twice as thick and even less permeable.

Best I can tell, all the aircraft in the blister database were painted with a urethane (from 7 different manufacturers). That doesn't mean the paint choice caused blisters. Heck, we want our paint to be impermeable as possible. However, if the diffusion rate of fuel molecules through the sealant is higher than the diffusion rate through the paint layer, well....
 
Sounds like time to build some sample tanks. I'd even consider building some without any sealant just to prove the paint will blister.
 
DanH said:
Best I can tell, all the aircraft in the blister database were painted with a urethane (from 7 different manufacturers). That doesn't mean the paint choice caused blisters.
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But it could indicate that the type of paint allows the blisters to form, regardless of what is causing them in the first place.
 
Mike S said:
But it could indicate that the type of paint allows the blisters to form, regardless of what is causing them in the first place.
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That's what I'm suggesting Mike. Earlier, more permeable paints probably allowed venting to the atmosphere.

We're talking about an increased rate here, not a never-before-seen event. Tank blisters have been around a long time. I recall a 1960's (?) blister story in a previous thread....Midget Mustang, T-18, something like that.
 
Is there a fix from the outside surface?

Just picked up my slightly used RV8 and workmanship in and out is beautiful, with real attention to detail. No blisters when I purchased her. I took my first cross country with her last week into a very hot climate, but kept her in a hangar there. I noticed one blister forming along the rear baffle rivets on the top right tank. A few days after returning home, 2 more in this area and a few on the bottom side of the left tank. Called the seller who shared that he had actually removed the tanks, had them professionally stripped and repainted due to the same issue previously. Obviously, while stripping and repainting this temporarily covered the issue, it did not resolve it. Looking inside the tanks, they appear to have sealant over every rivet shop end and good fillets. I pierced each blister with a syringe and found no fuel in any of them.

What to do? I read in a couple of posts that Loctite in the rivet head area appears to remedy the problem, call it a band aide, but when given the only other options, this appears to be reasonable choice, but does it really work? One could inject the Loctite under the blister and work out any excess. Can anyone share?
 
Mark, can you confirm a few points for the database?

I see you call Tucson home. Your new-to-you RV-8 was imported from a cool climate area?

You mentioned stripping and repainting. Is there any evidence or report of internal re-sealing?
 
Thanks Mike, My wife and I are pretty excited about the RV8 and love flying her. We are graduating from a Grumman Tiger.

No sign of re-sealing inside the tanks that can see. Just appears to be what I've seen in Rick's photos as a good job. Yes, she came from a cooler northern climate.
 
mspenc45 said:
No sign of re-sealing inside the tanks that can see. Just appears to be what I've seen in Rick's photos as a good job. Yes, she came from a cooler northern climate.
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Thank you Mark. If you elect a repair involving the removal of paint from the blisters, please contact me by email or PM.
 
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